Studies On Galactic Kinematics

We re-establish the Galactic coordinate system?GalCS?based on multi-wavelength catalogs,and determine the local standard of rest?LSR?using the Gaia TGAS astro-metric catalog and Gaia DR2 catalog.The kinematical properties of the Milky Way are also analyzed based on different stellar samples.The GalCS is a practical coordinate system for studies of the Milky Way.With all-sky data at different wavelengths released by AKARI and WISE,and the position of Sgr A*observed by VLBI,we construct a new GalCS that is directly connected to the International Celestial Reference System?ICRS?and consistent with the feature associated with the Milky Way.The revised parameters for defining the new GalCS in the ICRS are summarized as??P,?P?=?192°.777,26°.9298?for the equatorial coordinates of the north Galactic pole and ?=122°.95017 for the position angle of the Galactic center.The measurement of the solar peculiar motion with respect to the LSR is a matter of debate due to the fact that different samples were used.Adopting the astrometric data from the Gaia DR1 TGAS catalog,we present a full analytical study of the solar neighborhood kinematics,and select a stellar population having approximate dynam-ical-equilibrium state with known radial scalelength to estimate the solar peculiar mo-tion.Based on the Jeans equation we obtain?U?,V?,W??=?7.65 ± 0₄4,4.72 ±0.44,7.19 ± 0.28?km s-1.Employing the astrometric data and the measurements of the line-of-sight velocities of main-sequence stars from the recent released Gaia DR2 catalog,we obtain?U?,V?,W??=?8.63 ± 0.64,4.76 ± 0.49,7.26 ± 0.36?km s-1.The corresponding radial scalelength is?2.5 kpc.Combining the above results,we give an explicit recommendation for the LSR,which is parameterized by?U?,V?,W??=?7.96,4.74,7.22?km s-1.The rotation of the Milky Way traced by young populations is non-axisymmetric.Employing a dynamical model,we exploit the motion of the VLBI observed masers in high-mass star-forming regions and detect their rotation shape.In the solar neighbor-hood,the ellipticity of the average orbit is yielded as ?0?0.15?0.19.The azimuth of the major axis of the orbit is around 300°-400°.Based on the elliptical rotation model,we make a kinematical calibration of the Galactocentric distance of the Sun,which is yielded as R0?7.3 kpc.